To protect copyright of electronic documents including electronic books, multimedia etc. so as to protect bookman's rights and interests, the DRM technologies are adopted at present to protect electronic documents, such as electronic books and multimedia, from unauthorized play or unauthorized copy. The DRM technologies protect digital contents by encrypting electronic documents and appending application rules. And, the application rules may be adopted to determine whether a user meets requirements for applying the electronic documents.
In the prior DRM technologies, a problem of whether copies for electronic documents may be distributed is generally not taken into consideration so as to protect electronic documents from being copied or applied illegally. That is, after an electronic document is possessed, the electronic document may be merely opened in a limitative device, meanwhile distributing copies for the electronic document to others may be forbidden. Alternatively, the electronic document may be freely copied without any limitation. Neither of the two modes above may perform reasonable protection on documents.
It can be seen that, the prior DRM technologies cannot freely implement a distribution for copies for electronic documents on a certificate of protecting digital rights.